Catastrophic Decompression; Small Place Solo

"Jim Weir" wrote in message ...

Then you've never been around Oshkosh at dawn after a couple of six-packs and a
few cans of bean dip the night before.

Don't forget the cheese curds!

Bob Gardner wrote:

Gotta admit that I am working from memory of events many long years ago and
may easily have screwed up the details. With regard to the fog, however,
there has to be moisture from somewhere...simple expansion is not the whole
story. Fog is, after all, a gazillion eensy-teensy droplets.

When the pressure drops, the temperature drops. All that happened was you went
below the dew point in the chamber.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

"Aviation" wrote in message
For well trained pilots this
would take, what, only a few seconds at most? Do they put their oxygen
masks on FIRST or start the dive first?

At the most. They almost certainly put their maskes on first, but they are
of a "quick don" type that can be put on with one hand, so it's quite concievable
that they are already starting the dive concurrently with flipping the mask over
their face.

In some movies, the pilots are often unconscious, slumped over the
controls (wedging the 'steering wheel' / joystick full forward) as
the hero struggles to pull them out of the way and get out of the
dive. It sounds like a pilot, if not alert or in good health, could
actually lose consciousness from hypoxia under these conditions, so
maybe those kinds of movie scenes are ALMOST believable?

I believe that you've got a reasonable amount of time (30 seconds).
I can't vounch for whatever scenario you're specifically talking about.

For the movie Executive Decision,
they were cruising at 39,000 ft. so they'd have to dive 25,000 ft
to 14,000 ft in 5 minutes, 5,000 ft/minute, average. Doable?

5000 feet a minute isn't hard to obtain.

"Aviation" wrote in message

So, other than alarms or other signals, there is NOTHING AUTOMATIC
that puts the aircraft into rapid descent.

Correct.


Pilots have to respond to the signals... and initiate the dive MANUALLY.
For well trained pilots this would take, what, only a few seconds at most?
Do they put their oxygen masks on FIRST or start the dive first?

*Always* get the cockpit crew on O2 before anything else.


In some movies, the pilots are often unconscious, slumped over the
controls (wedging the 'steering wheel' / joystick full forward) as
the hero struggles to pull them out of the way and get out of the
dive. It sounds like a pilot, if not alert or in good health, could
actually lose consciousness from hypoxia under these conditions, so
maybe those kinds of movie scenes are ALMOST believable?

Not even remotly close to almost believable. Hollywood would have you
believe that there is an auto-trigger on all aircraft that renders the
engines non-functional, the aircraft uncontrollable, and the crew
unconscious whenever anything stressful occurs in the passenger cabin.
Truth is, if you're cruising at FL350 or higher you've only got about 5
seconds max to get the mask on, but it only takes about one to two seconds
to don the mask and get full O2 flowing. This is why crews train to an
instinctive reaction to get the mask FIRST. A person in average good health
will not have a problem with a few seconds of decompressing atmosphere. The
problem comes in on long flights. Toward the end, your day is already 12 or
more hours long, you're up high for efficiency - maybe 390 or 410 - which
means the cabin altitude is up around 9000 ft or more and everyone is tired.
Reaction time becomes crucial. When you're cruising high, a prudent crew
will ensure that the masks are preset and ready to go, and will don the O2
for a few minutes every little while just to make sure everyone stays alert.



Assuming
there is 3-5 minutes of mask-oxygen and one minute of "holding"
the last breath, they've got 3-6 minutes to get down to breathable
(14,000 ft?) air and then below. For the movie Executive Decision,
they were cruising at 39,000 ft. so they'd have to dive 25,000 ft
to 14,000 ft in 5 minutes, 5,000 ft/minute, average. Doable?

Absolutely. In an emergency descent, the prime (only) consideration is to
*get down safely*. The limiting factor is airspeed buildup. Airplanes are
very "slippery", and will build up speed at an impressive rate when allowed
to run freely downhill. In a rapid descent, you extend all the high drag
devices you can use (flaps, slats, spoilers, Ldg gear) to control airspeed
while you let the craft descend at the maximum vertical rate possible. In
the 747, the limit airspeed is 320 kt, (iirc) and that speed range's not
atypical for other transports, either. Typically, you'll see descent rates
of 10 to 15 thousand feet/minute.



The discussion of the ear problem seems unsettled..... Descending from
25,000+ (39,000) ft at 5,000 ft/min could result in reversible
or IRREVERSIBLE damage depending on a person's ability to
equilibrate REALLY fast.

When you get into emergency actions, you think in terms of minimizing or
prioritizing injuries. A rapid descent may well cause some passengers (or
crew) ear injuries, or even broken bones if they're not belted in. But the
alternative is substantially less desirable.

Read 91.211 for more info. There are conditions under which one pilot must
be wearing the mask under non-emergency conditions.

This reminds me of the time when LearJet got a jet certified for 51,000
feet...the photograph in the aviation press showed both pilots smiling into
the camera at FL510 without an oxygen mask in sight. Always wondered how the
FAA reacted to that.

Bob Gardner

"Aviation" wrote in message
u...
Thank you, everyone, for providing lots of helpful answers and info.

Even with slightly inaccurate info (2-seater; 6-seater), I guess
the second Q was easy:
Is the simplified movie solo flight completely
bogus or could it happen that way?

The basic answer is "more or less".

The answers to the first Q, being more tecnically compicated, leave
me asking for a few clarifications. That was about what REALLY happens
when a large pressurized aircraft, e.g., a 747, explosively or
catastrophically decompresses at high (25000+ feet) altitude.

Ron Natalie ) wrote:
On the one hand, passengers need to get denser air to breathe
but large aircraft have oxygen masks that drop down.

The pilots initiate the dive for the reasons you suggest. While
supplemental oxygen helps, it's still better to get down to a reasonable
altitude. They presmably notify ATC while they are doing
this that there is an emergency in progress.

So, other than alarms or other signals, there is NOTHING AUTOMATIC
that puts the aircraft into rapid descent. Pilots have to respond
to the signals (explosion, screams from the cabin, meters in their
cockpit, their own ears popping, flashing lights, bells and whistles,
etc.) and initiate the dive MANUALLY. For well trained pilots this
would take, what, only a few seconds at most? Do they put their oxygen
masks on FIRST or start the dive first?

In some movies, the pilots are often unconscious, slumped over the
controls (wedging the 'steering wheel' / joystick full forward) as
the hero struggles to pull them out of the way and get out of the
dive. It sounds like a pilot, if not alert or in good health, could
actually lose consciousness from hypoxia under these conditions, so
maybe those kinds of movie scenes are ALMOST believable?

(This assumes worst case total decompression. It was pointed out
by Mike Rapoport ) that the cabin might
not even go to ambient pressure if the hole isn't too big and the
outflow valves close down and the engines keep pumping air into the
cabin.)

Someone also pointed out my goof about "holding" your breath
upon going from cabin (8000 ft pressure) to ambient (25-35,000
ft pressure). In estimating how much time the average civilian
passenger could go without TAKING a breath of good air (14,000
ft or below), I used the HOLD your breath estimate. Assuming
there is 3-5 minutes of mask-oxygen and one minute of "holding"
the last breath, they've got 3-6 minutes to get down to breathable
(14,000 ft?) air and then below. For the movie Executive Decision,
they were cruising at 39,000 ft. so they'd have to dive 25,000 ft
to 14,000 ft in 5 minutes, 5,000 ft/minute, average. Doable?

I found some rate of ASCENT data of about 3850 ft/min at
http://www.altairva-fs.com/fleet/poh...0747%20POH.htm
but descent data isn't clear to me but it looks like 2500 ft/min
from cruise altitude down to 10,000 ft is the recommended ROD.

The discussion of the ear problem seems unsettled. Upon going
from 8000 ft cabin pressure to 25000+ ft pressure in a couple
of seconds (if loss of pressure is total), some rapid swallowing
should equilibrate your ears to low pressure. Descending from
25,000+ (39,000) ft at 5,000 ft/min could result in reversible
or IRREVERSIBLE damage depending on a person's ability to
equilibrate REALLY fast. Apparently, some people posting have
done this during training in hyperbaric chambers.

Once again, THANK YOU for your answers. Even tho' I'm annoyed
or perplexed by a lot of Hollywood pseudoscience, I get extra
value from these usenet discussions.

Have a Happy New Year.






--
Sent by xanadoof from yahoo included in com
This is a spam protected message. Please answer with reference header.
Posted via http://www.usenet-replayer.com

"John Gaquin" wrote
Truth is, if you're cruising at FL350 or higher you've only got about 5
seconds max to get the mask on, but it only takes about one to two
seconds to don the mask and get full O2 flowing.

From the following web site:

http://www.sff.net/people/Geoffrey.Landis/vacuum.html

A larger body of information about how long you would remain conscious comes
from aviation medicine. Aviation medicine defines the "time of useful
consciousness", that is, how long after a decompression incident pilots will
be awake and be sufficiently aware to take active measures to save their
lives. Above 40,000 feet (12 km), the time of useful consciousness is 12 to
25 seconds. (The shorter figure is for a person actively moving; the longer
figure is for a person sitting quietly.)

The number that we were always taught in the airline business was that at
39,000', the time of useful conciousness was 18 seconds.

Bob Moore

"Bob Gardner" wrote

This reminds me of the time when LearJet got a jet certified for 51,000
feet...the photograph in the aviation press showed both pilots smiling
into the camera at FL510 without an oxygen mask in sight. Always
wondered how the FAA reacted to that.

They probably had "quick donners" available, which modifies the reg.

Bob Moore

Yes, I got results on the carbon fiber and I would have SWORN that I posted them
to this site.

Putting a GPS antenna UNDER a small bowl-shaped carbon fiber radome immediately
killed any GPS signal into a 27 dB gain active antenna INCLUDING satellites that
were directly overhead.

Figuring that the carbon was so lousy a transmissive path, I drilled a hole on
the top of the bowl and used the bowl as the groundplane. VIOLA. The GPS
antenna worked every bit as well on TOP of the carbon fiber as it did on a metal
ground plane of approximately the same size.

I can't say this is true for any other service than GPS (transponder, vhf nav &
com, etc.) but it did test well for GPS.

Jim



Richard Riley
shared these priceless pearls of wisdom:

-
-Did you ever get results on the carbon?

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Was that in reference to a stray bullet causing the decompression?
If so, I'd have to agree that he's full of it.

Yes, just so. He agreed that the sky marshal would have frangible
bullets, but argued that the terrorist would not. That would lead to a
bullet through the airplane (he didn't specify window, which I
understand to be a problem) followed by explosive decompression "and
all that that entails."

all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

"Robert Moore" wrote in message

Above 40,000 feet (12 km), the time of useful consciousness is 12 to
25 seconds. (The shorter figure is for a person actively moving; the
longer
figure is for a person sitting quietly.)

The number that we were always taught in the airline business was that at
39,000', the time of useful conciousness was 18 seconds.

Bob, I was taught similar numbers. I based my estimate solely on anecdotal
reference provided by two friends, each of whom had "enjoyed" a rapid
decompression at high flight level -- one at 390 and one at 410. The fellow
at 390 was out of his seat getting coffee (small galley immediately behind
the jump seats on 747 freighters) when the cabin blew. They both related
similar sensations. They went right for the masks, and had them on quickly
[estimated 2-3 seconds for the guy in his seat, and 3-4 seconds for the
coffee drinker], but each said they felt "spacey" almost immediately. A
combination of fatigue, confusion, forced exhalation, etc., left each of
them, in separate instances, with the conviction that at somewhere around 10
seconds or so they probably would have lost the mental discipline to stay
focused and get the damn mask on. I have no personal experience that would
allow me to comment on their remarks.

John Gaquin